While this question looks quite simple and sort, it can be deceptively complicated. Here is a good answer:
The smell of the pizza in our room travels there through the process of diffusion. Diffusion is the process of molecules spreading out from a high concentration to a low concentration. When the cooks put the pizza in the ovens, they are creating a high concentration of pizza smell molecules down there. If diffusion dictates that they must spread out, then the smell will travel through the school, spreading into areas like our classroom where the pizza smell molecules are at a low concentration. In a few hours, the concentration of pizza smell molecules will reach a concentration that we can smell.
The smell of the pizza in our room travels there through the process of diffusion. Diffusion is the process of molecules spreading out from a high concentration to a low concentration. When the cooks put the pizza in the ovens, they are creating a high concentration of pizza smell molecules down there. If diffusion dictates that they must spread out, then the smell will travel through the school, spreading into areas like our classroom where the pizza smell molecules are at a low concentration. In a few hours, the concentration of pizza smell molecules will reach a concentration that we can smell.